There have been numerous brake systems developed for stopping hydraulic ram elevators during emergency situations. All of the prior art patents found were directed toward collets that during a hydraulic pressure failure would drop down and wedge in between a fixed housing and the ram of the elevator. The friction generated by the downward motion of the ram in contact with the collet or brake shoe causes the collet or tapered brake shoe to be driven downward, thereby wedging the ram to a halt. Empirical evidence indicates that the force necessary to stop an elevator using a brake of this type exceeds the elastic limit of the material used to construct commercial rams. As a result, the ram may be deformed into an hourglass shape at the point where the brake grips the ram. Since this type of damage to the ram cannot be repaired, the ram and in some instances its associated components must be replaced in order to restore the elevator to working condition. Replacement of the ram is time consuming and expensive.
Because the elevator brakes disclosed in prior art patents have a relatively large number of moving parts, they are relatively complex. Additionally, the prior art devices are relatively large and bulky. In designing a brake system, size is an important consideration because there is often limited space into which to fit a braking device. Therefore, in order to facilitate installation of new brake systems into hydraulic elevators, it is desirable for them to have a low profile.
A specific example of a prior art design having the above mentioned shortcomings is Beath et al., U.S. Pat. No. 4,449,615, which discloses a floor mounted lever-actuated wedge device. The many components in this design complicate it by comparison to the present invention. Beath uses a collet design. During certain conditions, such as a hydraulic pressure failure, the collets will drop down and wedge in between a fixed housing and the ram of the elevator. The friction generated by the downward motion of the ram in contact with the collets causes the collets to be driven downward. As this occurs, the collets are wedged against the ram. The contact between the collets and ram generates a friction force which slows the ram and eventually becomes great enough to stop the descent of the ram. The force necessary to stop an elevator using the brake disclosed in Beath exceeds the elastic limit of the material used in commercial rams. As mentioned above, this causes the ram to deform into an hourglass shape at the point where the collets grip the ram. In regard to the importance of braking systems having a relatively low profile, the above mentioned patent does not precisely show the relation of the system to the top of the cylinder and the bottom of the elevator. However, it appears too tall to fit most existing elevator systems. In light of the problems discussed above and exemplified by U.S. Pat. No. 4,449,615, a new elevator brake is needed that can safely stop a fully loaded elevator without permanently damaging the ram. A control system for such a new elevator brake is also needed.